1. Field of the Invention
The present invention relates to a process for refining sulfur contaminated hydrocarbon feedstocks. More particularly, the invention concerns a process wherein organic sulfur compounds are removed from said feedstocks in the form of hydrogen sulfide by contacting said feedstocks, in the presence of hydrogen, with a catalyst system comprising a difficulty reducible metal halide and a hydrogen halide.
2. Description of the Prior Art
It has long been recognized that the presence of impurities such as sulfur, metals, nitrogen, oxygen, resins, and the like in hydrocarbon feedstocks tend to poison or deactivate acidic catalysts which contain a refractory oxide, a noble metal, and a Lewis acid and/or a Bronsted acid component. Such catalysts may be used in reactions such as reforming, alkylation, isomerization and the like. To overcome this problem, it has been proposed that such impurities, particularly organic sulfur compounds, may be removed from hydrocarbon fractions, preferably during the hydrocarbon reaction process, by reaction in a suitable solvent. The solvent may be in either the liquid or in the vapor phase. Suitable solvents include hydrogen fluoride, boron trifluoride, sulfur dioxide and others, alone or in combination (see for example Br. Pat. No. 292,932, U.S. Pat. Nos. 2,343,841; 2,440,258; 2,450,588; 2,465,964; 2,519,587; 2,564,071 and 2,643,971).
A combination process for removing sulfur from hydrocarbon fractions is described in U.S. Pat. No. 2,689,207. In this process, the sulfur is extracted from said hydrocarbon fractions with hydrogen fluoride, the sulfur-containing extract thus formed being sent to a separate hydrogenation step wherein the sulfur in said extract is converted to hydrogen sulfide. The hydrogen sulfide is then removed, leaving a sulfur-free hydrogen fluoride/hydrocarbon liquid (the hydrocarbon extracted with the sulfur) which is recycled to the extraction stage for blending and further contacting with the original hydrocarbon fractions. More resently, U.S. Pat. No. 3,123,550 disclosed a process for removing nitrogen from distillates by hydrotreating a mixture of the distillate and a mineral acid (such as a hydrogen halide) over a supported hydrogenation catalyst.
In addition, processes involving the use of metal halide based catalysts have also been described in the prior art. For example, U.S. Pat. Nos. 2,683,763 and 2,683,764 disclose that colombium (niobium) pentafluoride or tantalum pentafluoride in combination with hydrogen fluoride can be used to refine hydrocarbon oils. In particular, sulfur compounds complexed with the metal fluoride-hydrogen fluoride catalyst are separated therefrom by heating to first remove the hydrogen fluoride, followed by subsequent dissociation of the sulfur compounds from the metal halide upon further heating. An article by Fairbrother, F. et al., J. Chem Soc., pp. 765-770, 1965 mentions the composition of tantalum pentafluoride-organic sulfur compound complexes which dissociate upon heating at temperatures below about 100.degree. C. Another article by Olah, G. A. et al., J. Amer. Chem. Soc., Vol. 89, pp. 2296-3301, June 7, 1967 describes the protonation and cleavage of organic sulfur compounds using a fluorosulfonic acid-antimony pentafluoride catalyst system.
However, none of the foregoing prior art teaches or suggests a process for hydrodesulfurizing the organic compounds in a hydrocarbon feedstock in the presence of a metal halide-hydrogen catalyst.